The present invention relates to a refrigeration or air conditioning system, and more particularly, to a refrigerant system configured to operate at multiple capacity modes.
Refrigeration and heating or air conditioning systems (commonly called refrigerant systems) are generally configured with means for system unloading, thereby allowing the systems to improve temperature control accuracy, reliability, and energy efficiency.
Currently the most common means for system unloading is accomplished by unit cycling (i.e., turning the compressor on and off). However, unit cycling does not allow for tight temperature control, and therefore, commonly creates discomfort and/or undesired temperature variations if used to cool an occupied space. Additionally, unit cycling introduces system inefficiencies associated with unit cycling losses and the system must operate with a high refrigerant mass flow rate when the compressor is turned on.
A suction modulation valve is another means commonly utilized for system unloading. With a suction modulation valve unloading is accomplished by limiting the amount of refrigerant flow by partially closing the suction modulation valve. However, a suction modulation valve is relatively expensive and is inefficient for system capacity control due to flow throttling losses when the valve is in a partially closed position.
U.S. Pat. No. 7,353,660 to Lifson et al. discloses a multi-temperature cooling system with unloading. However, this system does not vapor inject refrigerant into an inter-stage of a multi-stage compressor assembly to achieve unloading. Additionally, the flow of refrigerant through the suction line from evaporator 68 to the port 54 of the compressor 52 cannot be throttled by a valve and directed through a bypass line to be injected into the inter-stage of the compressor to achieve unloading.
U.S. Pat. No. 6,860,114 to Jacobsen discloses a system capable of operating at different operational cooling stages. However, the valve 144 Jacobsen discloses in the bypass line is a check valve which only allows refrigerant to flow in one direction. Thus, the opening of valve 144 is controlled solely by pressure differential across it. Because valve 144 requires a specific pressure differential to open, both valve 144 and valve 134 cannot be opened simultaneously to achieve unloading by allowing refrigerant flow to both the first and second stages of compressor 60.